1. Field of the Invention
The present invention relates to a pixel structure, particularly relates to a pixel structure having a red sub-pixel, a green sub-pixel, a blue sub-pixel and a white sub-pixel.
2. Description of Related Art
As technology constantly advances, expectations of display quality of displays by people continuously increase. Not only are images of the displays desired to have high resolutions, high brightness and high contrast, displays are also desired to have advantages of light weight and low energy consumption. In conventional liquid crystal display (LCD) panels, a pixel structure thereof includes a red sub-pixel, a green sub-pixel and a blue sub-pixel. However, in LCD panels of portable electronic products, a pixel structure thereof may include a red sub-pixel, a green sub-pixel, a blue sub-pixel and a white sub-pixel. The white sub-pixel with high transmittance enhances overall brightness of the LCD panel, thereby reducing energy consumption of a backlight module. Hence, a multi-primary color display may also adopt a yellow sub-pixel other than the red sub-pixel, the green sub-pixel and the blue sub-pixel or other sub-pixels having higher transmittance to enhance overall brightness of the LCD panel, so as to reduce energy consumption of a backlight module.
Generally, color images displayed by the LCD panel must meet requirements of a manufacturer or international standards. In detail, under circumstances of using a D65, a D50 or a 9300K light source, a chroma coordinate of a white light displayed by the LCD display having the red sub-pixel, the green sub-pixel and the blue sub-pixel must be within a specific range, so that a correct white balance can be achieved. When the LCD panel has the red sub-pixel, the green sub-pixel, the blue sub-pixel and the white sub-pixel, the chroma coordinate of the white light displayed must also be within the above specific range. However, the chroma coordinate of the white light often shifts. At this moment a ratio of areas of the sub-pixels of different colors is modified (for example in U.S. Pat. No. 7,256,855 B2), or a spectrum of the backlight module is adjusted (for example in U.S. Pat. No. 6,989,876 B2), so that color shift of the white light is prevented to obtain the correct white balance.
Referring to FIG. 1, U.S. Pat. No. 7,256,855 B2 changes an area of the blue sub-pixel B, so that the area of the blue sub-pixel B is larger than an area of the green sub-pixel G and an area of the red sub-pixel R in order to increase ratio of blue light in the displayed image, thereby improving a phenomenon of the yellowish image.
In addition, in U.S. Pat. No. 6,989,876 B2, the spectrum of light emitted from the backlight is adjusted to solve the problem of color shift. In U.S. Pat. No. 6,989,876 B2, the spectrum of light emitted the backlight module used thereof is shown as spectrum blue 1.09 and spectrum blue 1.18 in FIG. 2. Compared with the spectrum blue 1, the spectrum blue 1.09 and the spectrum 1.18 have higher energy in a range of blue wavelengths and have lower energy in a range of red wavelengths, so that the spectrum blue 1.09 and the spectrum 1.18 may reduce a phenomenon of the yellowish image.
A chroma coordinate of a white light provided by a currently used white light-emitting diode is within an area surrounded by thick lines in FIG. 3. When the white light-emitting diode is used as a light source of the backlight module, chroma coordinates of red light, of green light, of blue light and of white light that may be generated by currently used red, green and blue filter films are shown in FIG. 4. When a color space to be displayed by the display panel is larger, color saturation of the red light, the green light and the blue light needs to be higher. At this moment, a y coordinate of the red light is smaller, an x coordinate of the green light is smaller, and both an x coordinate and a y coordinate of the blue light are smaller, and after color mixing, an x coordinate and an obtained y coordinate of the obtained white light are smaller. Therefore, the white light displayed by the display panel shifts towards blue-green. If the white balance is to be adjusted to within a predetermined range, the light emitted from the white light-emitting diode must shift towards red-orange. However, as limited by specifications the white light-emitting diodes currently produced, the white light-emitting diode that meets the above-mentioned requirements is difficult to purchase. Hence, methods of adjusting the backlight to improve the problems of the color shift are already facing a technological bottleneck.
Accordingly, no matter modifying the ratio of the areas of the pixels or adjusting the spectrum of the backlight module, costs and technical difficulties thereof have relatively increased.